ubuntu-manual team mailing list archive

[Jonathan Marsden <jmarsden@xxxxxxxxxxx>]

On 06/15/2013 09:59 PM, Kevin Godby wrote:

>>    * Use set -e to exit when an error occurs.

> Does this interfere with the "try_this_command || handle_the_error"
> parts of the script?

No, only if a whole command line fails will it take effect.  I did have
to modify some places where the script did something like

  echo "$PKG" |grep -q ","
  EXIT_STATUS=$?
  if [ $EXIT_STATUS -eq 0 ]; then

because the grep in first of these lines would fail "on purpose"
sometimes, causing the script to exit.  So I turned this into the
(shorter, easier to read, and slightly more efficient, IMO)

  if [[ "$PKG" =~ "," ]]; then

instead, in two or three places.  man bash says:

    -e      Exit immediately if a pipeline (which may consist of a
            single simple command), a subshell command enclosed in
            parentheses, or one of the commands executed as part of a
            command list enclosed by braces (see SHELL GRAMMAR above)
            exits with a non-zero status.  The shell does not exit if
            the command that fails is part of the command list
            immediately following a while or until keyword, part of the
            test following the if or elif reserved words, part of any
            command executed in a && or ⎪⎪ list except the command
            following the final && or ⎪⎪, any command in  a pipeline
            but the last, or if the command's return value is being
            inverted with !.

>>    * Sort and remove duplicates from package list.

> That's fine, though it's unnecessary as apt-get will take care of
> that for us.

True, but since I wanted to display it, it helps readability a lot :) :)

>>    * Display package list before downloading and installing packages.

> Good idea. I haven't looked at your script code yet, but you could
> just allow the output from apt-get to be displayed on the screen so
> the user can see the download/install progress, too.

I thought about doing that, but you had apparently deliberately hidden
that output, so I decided there must be a reason for that choice...  I
didn't want to trample on your design choices :)

Jonathan